One must always remember that the birds haven't read the books or
seen the distribution maps.
The populations of Crimson and Yellow Rosellas can be thought of as
occupying a curved distribution, with the Yellow form along the Murray
and the Crimson further south. The Adelaide Rosella certainly occurs
where these forms meet and overlap - after all the mouth of the Murray
isn't far from Adelaide at all. Years ago, I recall noticing that young
Crimson Rosellas in the Little Desert were a much yellower green than
those I knew in Melbourne. Crimson Rosellas certainly occur in the Mt.
Lofty Ranges, but I don't remember anything special about their
colouring. We saw Adelaide Rosellas there too.
Adelaide Rosellas are quite variable - many are much redder or much
yellower than the typical form illustrated in the books.
I understand that the two forms meet at the eastern end of their range
around Albury but here the Crimson and Yellow do not interbreed to form
natural hybrids. Textbooks call this type of distribution a 'species
chain' or 'circle' or 'Rassenkreis'. The textbook example is the
interrelationships of gulls right round northern Europe and America -
which I can't quote from memory. The Herring Gull is one end of the
chain.
An Adelaide Rosella has been seen at times in Wilson Reserve near my
home in Ivanhoe (Vic) for a few years now. It is a very handsome bird -
presumably an escape.
Anthea Fleming
Gary Davidson wrote:
>
> I'm hoping someone can clear up a taxonomy question for me. I was
> looking at the 'blue-ckeeked' Rosellas in Pizzey and Knight and I see
> that the the "Adelaide" Rosella is described as a natural hybrid of
> Crimson and "Yellow" Rosellas. But the range of the Adelaide Rosella
> is clearly to the west of the other two, and does not overlap at all
> with Crimson. How can a subspecies that is the result of
> hybridization of two others, have a separate distribution?
> Gary
>
> ----------------------------------------------------------------------
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